One of the worst things that can happen to you in this technical era is after doing a whole load of work on a report for work, university or school to loose it after a hard drive decides to die, gets water poured on it, or stolen. All the parts are replaceable, for a little expense, however the work that has just been done - gone, the photos, the music, et al gone. It's not fun! So there are a couple of methods of backup to prevent this problem.
External Hard Drives - Local Backup
Getting an external hard drive is one of the best form of backup for either a personal computer or a laptop. Simply plug the external drive into the computer, copy across the files to the drive and then store in a safe place. Both Windows Seven and Apple's OS X have backup software built in, so all you need to do is to tell it where the hard drive is!
Getting an external drive doesn't have to be expensive either, Freecom sell a fantastic little 250Gb hard drive which you can pick up from Amazon for just £39.99. Having this drive means that you can carry your important files wherever you need them; to and from the office, etc, and have a brilliant back up just incase something goes wrong.
Cloud Based Backup - Off Site Backup
The external backup system is great, and protects you against hard drive failure. However if you get burgled, and the thief takes both the computer and the external hard drive, then you are no better off. This is why off site back up is so important. One method is to buy a second external hard drive and ask someone you know to look after it, this is a good enough method, however a little bit of a pain to swap drives over, etc. A better method is to store your data online. There are various internet services such as Apple's Mobile Me, Amazon's S3, etc that will allow you to backup your data online.
The best service I've found so far is a service called Dropbox. Dropbox is a service that gives you 2Gb of file space on the internet. It is a small little program that you install on one or more computers, it creates a folder, which you can place any folder or file into, as soon as you do it automatically copies it to their servers, all backed up. This also means that if you need access to the files saved in the Dropbox on your other computer, your friend's computer or even your iPhone or Android Phone you can simply log in to Dropbox and get access to these files. It is very very handy. I use it every day and highly recommend it. Go get it!